Question

Which thermocouple can be used to measure $1500^{\circ}\text{C}$ temperature?

• A. Copper constaton
• B. Chromel alumel
• C. Platinum rhodium
• D. Iron constanton

Hint:

Noble metal thermocouples (Platinum-Rhodium, such as Type R, S, and B) are reserved for extreme high-temperature environments.
Base-metal thermocouples (J, K, T, E) are cheaper but melt or degrade at temperatures above $1200^{\circ}\text{C}$.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
This question asks us to identify which type of thermocouple is physically and chemically capable of measuring extremely high temperatures up to $1500^{\circ}\text{C}$.

Step 2: Detailed Explanation:

• Different thermocouple material combinations have different temperature measurement limits, stability, and oxidation resistances:

• Copper-Constantan (Type T): Suitable for low-temperature applications, typically ranging from $-200^{\circ}\text{C}\text{ to }350^{\circ}\text{C}$.

• Iron-Constantan (Type J): Limited to temperatures up to approximately $750^{\circ}\text{C}$ due to the oxidation of the iron wire.

• Chromel-Alumel (Type K): A popular base-metal thermocouple used for temperatures up to about $1200^{\circ}\text{C}$. At $1500^{\circ}\text{C}$, it degrades rapidly.

• Platinum-Rhodium (Type R, S, or B): These are noble-metal thermocouples. Type R and Type S use Platinum-Rhodium alloys and can continuously measure temperatures up to $1600^{\circ}\text{C}$ (and up to $1700^{\circ}\text{C}$ for Type B) in oxidizing or inert atmospheres.

• Therefore, for measuring high temperatures like $1500^{\circ}\text{C}$, noble metal thermocouples containing Platinum and Rhodium must be used.

Step 3: Final Answer:
The thermocouple that can be used to measure $1500^{\circ}\text{C}$ is the Platinum-Rhodium thermocouple.